1. Field of the Invention
The present invention relates to a printed wiring board, and more particularly to a multi-layered printed wiring board having, inside of a substrate, a power source layer (power source layers) for supplying electric power to a semiconductor device.
2. Description of the Related Art
Conventionally, undesirable electromagnetic wave noise generated inside an electric or electronic device or external noise entering from the outside into an electric or electronic device has been a serious problem for electric and electronic devices. For this reason, electromagnetic compatibility (EMC) design is necessary in order to prevent undesirable electromagnetic wave noise from being generated inside the electric and electronic devices and to secure strength against external noise.
In recent electric and electronic devices, digitization of their electronic circuits and acceleration of the processing speed have been achieved. Accompanying this trend, electromagnetic noise has also increased rapidly. Further, due to the rapid increase in use of cellular phones, external noise has also increased. For this reason, EMC design has becomes technically difficult.
Particularly, a source of electromagnetic wave noise recently considered to be an important problem is noise current, which flows into a power source layer inside a substrate from a power supply circuit for supplying electric power to the semiconductor device when switching the semiconductor device which is disposed on the substrate.
According to Japanese Patent Application Laid Open (JP-A) No. 5-13909, a circuit board having a main power plane, a ground system, a very large scale integrated device and a sub-power plane has been proposed in order to suppress such noise current. As shown in FIG. 12, a main power plane 60 and a sub-power plane 62, which is physically separated from the main power plane 60 and which is supplied with electric power from the main power plane 60 through a filter 64, are provided as power source layers. The sub-power plane 62 is disposed just below a very large scale integrated device 70 and supplies electric power to the very large scale integrated device 70.
In the same way as the aforementioned JP-A No. 5-13909, in the multi-layered printed wiring board proposed in JP-A No. 7-45962 which has a power source layer and a ground layer as the inner layers, the power source layer region, which is a connecting region of mounted components, and the ground layer region are separated and isolated from each other so as to prevent noise from being spread around.
However, although these prior art are effective for reducing radiation of low-frequency noise of not more than around 500 MHz which is generated from a circuit substrate when supplying electric power to the semiconductor device, it has been found that the radiation of high-frequency noise of about 1 GHz is great, or cannot be reduced.
An object of the present invention is to provide a printed wiring board capable of suppressing not only radiation of low-frequency noise but also radiation of high-frequency noise, so that undesirable radiation noise which is newly generated can be kept to a low level, thereby reducing noise to a large extent overall.
To achieve the above object, according to a first aspect of the invention, there is provided a printed wiring board for supplying electric power from an external power source to a semiconductor device, wherein the semiconductor device has a plurality of input power supply terminals for inputting substantially equal voltages to the semiconductor device, the printed wiring board comprising:
(a) a plurality of layers, the layers including:
(i) a mounting face having a plurality of electrical terminals, the mounting face being adapted for mounting the semiconductor device thereto with the plurality of semiconductor device power supply terminals electrically connected to the mounting face electrical terminals; and
(ii) another layer having a first power source region adapted for connection to the external power source; and
(b) a second power source region having an outer configuration smaller than an outer configuration of the semiconductor device, electrically insulated from the first power source region except through an electrical connection through a filter, and electrically connected to the mounting face electrical terminals for supplying electrical power received from the first power source region through the filter, to the semiconductor device.
According to the first aspect of the present invention, the second power source region for supplying electric power to a semiconductor device having plural input power supply terminals, to which the same voltages are inputted, is provided independently of the first power source region. As a result, low-frequency noise components of electric power supplied from the outside can be reduced, further, because the outer configuration of the second power source region is smaller than the outer configuration of a device to be mounted on the mounting face, high-frequency noise radiated from the second power source region can be suppressed to a low level.
Therefore, the radiation noise on the whole can be reduced to an extremely low level. The semiconductor device may be, for example, an integrated circuit component such as an LSI or a ULSI. The xe2x80x9csemiconductor device having plural input power supply terminals to which the same voltages are inputtedxe2x80x9d in the present invention means a semiconductor device having a set of plural input power supply terminals or plural sets of the plural input power supply terminals.
An effect of the present invention arises because the second power source region is smaller than an outer configuration of the semiconductor device. If the semiconductor device to be mounted is an integrated circuit component having a semiconductor chip or a die incorporating an integrated circuit, it is preferable that the second power source region is substantially as large as an area of the semiconductor chip contained in the integrated circuit component. Further, the second power source region may be rectangular, or may be a shape having roundness such as an oval, a circle or a rectangle having rounded corners. A shape having roundness can reduce radiation of noise correspondingly to the absence of angular corners.
Further, a single second power source region may be provided, or plural second power source region may be provided. Namely, one second power source region may be provided so as to correspond to one semiconductor device mounted on the mounting surface, or plural second power source regions may be provided so as to correspond to one semiconductor device mounted on the mounting surface.
For example, if plural function cells such as transistors or diodes are provided on a semiconductor chip within a semiconductor integrated circuit component selling as a semiconductor component, plural second power source regions can be provided electrically independently of one another such that one second power source region corresponds to one function cell or to plural function cells. Further, the second power source region for supplying electric power for the I/O of the semiconductor device and the second power source region for supplying electric power for the core may be provided separately.
Further, the first power source region and the second power source region may be formed on separate layers or on the same layer. If the first power source region and the second power source region are formed on the same layer, the effect of radiation noise reduction is more considerable than when they are formed on separate layers.
If the first power source region and the second power source region are formed on the same layer, the first power source region and the second power source region may be provided so as to be side by side, or the first power source region may be provided with an opening and then the second power source region may be provided within the opening such that it is not in direct contact with the first power source region.
As for the electrical connection between the semiconductor device and the second power source region, if plural external connecting terminals are provided on a rear face of the package like a ball grid array type semiconductor device, at the external connecting terminals may be connected directly to via holes for connecting to the second power source region. Or, in the case of a semiconductor device in which the external connecting terminals are provided along the periphery of the package, pins of the semiconductor device may be connected to the auxiliary wires, ones of ends of which are connected to the second power source region.
Preferably, the printed wiring board, wherein the second power source region is included in one of the layers, another layer includes auxiliary wires which supply electrical power received from the second power source region to the mounting face electrical terminals, first electrical connections connecting the second power source region to the auxiliary wires, second electrical connection connecting the plurality of input power supply terminals and auxiliary wires to one another, and an electromagnetic field separating portion through which at least one of the first and second electrical connections extends.
In other words, if the electromagnetic field separating portion is provided at least in the first interval, i.e., ifthe electromagnetic field separating portion is provided at least between the auxiliary wires and the second power source region, the electromagnetic field generated by the auxiliary wires and the electromagnetic field generated by the second power source region are separated. Consequently, the second power source region and the auxiliary wires are integrated with each other electromagnetically, so as to suppress radiation of noise.
The electromagnetic field separating portion provided in the first interval acts to separate the electromagnetic field generated by the second power source region and the electromagnetic field generated by the semiconductor device. Further, the second power source region and the semiconductor part are integrated electromagnetically so as to suppress radiation of noise. Of course, if an electromagnetic field separating portion is provided both in the first interval and the second interval, the second power source region and the semiconductor device are separated electromagnetically in two stages, so that a more marked effect can be obtained.
The electromagnetic field separating portion may be formed by a layer connecting member such as a via hole for connecting the auxiliary wires to the second power source region, or a layer connecting member such as a via hole for connecting the auxiliary wires to the semiconductor device.
Preferably, the printed wiring board, wherein the plurality of layers includes a ground layer forming a part of the electromagnetic field separating portion, and said at least one of the electrical connections extends through the ground layer.
That is, the sectional area of the via hole is very small as compared to the area of the second power source region. Thus, it is difficult for high-frequency noise components to pass through the via hole, and the via hole (layer connecting member) plays the role of inductor L.
If the first power source region and the second power source region are formed on the same layer, the reason why high-frequency noise components increase or cannot be reduced is that radiation noise leaks from the periphery of an annular slot specified by an opening formed in the first power source region and the periphery of the second power source region, because the second power source region is provided independently of the first power source region. It is noted that radiation noise increases as the site of the annular slot increases. Thus, the printed wiring board, wherein the layer having the first power source region also includes the second power source region, and the first power source region has an opening with an area less than the semiconductor device, and the second power source region is located in the opening.
That is, by decreasing the opening area of the first power source region to reduce the length of the periphery of the annular slot, radiation noise leaking from the periphery of the annular slot is prevented from becoming large. As compared to a case where the opening area is larger than the mounting face for the semiconductor device, the area of the annular slot is small, thereby making it possible to reduce generation of radiation noise. Because the second power source region is provided in an opening smaller than the outer configuration of the semiconductor device to be mounted on the mounting face, the area of the second power source region is smaller than the mounting face. As a result, noise radiated from the second power source region can be kept to a low level.
Preferably, the printed wiring board, wherein the auxiliary wires are included on the mounting face.
In case where the semiconductor device to be mounted is a ball grid array semiconductor device, the auxiliary wires are provided to be connected to a predetermined number of electrode pads among the electrode pads which are disposed two-dimensionally on the mounting face. With such a structure, the necessity of forming the auxiliary wires while avoiding the electrode pads and via holes is eliminated, thereby facilitating the wiring design. Consequently, the aforementioned effects can be obtained stably.
Further, by providing the auxiliary wires with capacitors at one end or both ends thereof, high-frequency current can be supplied stably, thereby suppressing generation of electromagnetic field noise from the semiconductor device.
Examples of the filter portion for reducing noise generated from electric power from the first power source region include an L-type filter, a xcfx80-type filter and an inductor L. The inductor L contained in the L-type filter, the xcfx80-type filter and the inductor L may be an inductor having only a reactance component, or may be a ferrite chip inductor having a resistance component may be used. The ferrite chip inductor results in a more marked noise reduction effect.
The filter portion may include: the printed wiring board of the first aspect, wherein the filter includes: a connecting portion connecting the first power source region and the second power source region to one another; and a narrow conductive path formed in the first power source region by a groove pattern for introducing electric power from the first power source region to the connecting portion. In this case, because the filter portion is formed in a portion of the first power source region, an additional part does not have to be provided as the filter portion. Therefore, the space for providing the filter portion becomes unnecessary. Consequently, the structure can be simplified and the cost for the filter portion can be eliminated.
Further, to achieve the above object, according to a second aspect of the present invention, there is provided a printed wiring board comprising: a printed wiring board for supplying power from a power source to an integrated circuit component, wherein the integrated circuit component includes a plurality of input power supply terminals for inputting substantially equal voltages thereto, the printed wiring board comprising a substrate including:
a mounting surface having electrical contacts, and adapted for receiving the integrated circuit component on the mounting surface, with the power supply input terminals of the integrated circuit component electrically connecting to the mounting surface electrical contacts;
a first power source region having an opening of an area less than the integrated circuit component;
at least one second power source region provided in the opening independent from the first power source region, with the second power source region connected through a filter portion to the first power source region;
a ground layer; and
auxiliary wires provided on the mounting surface, each auxiliary wire having opposite ends with one end connected to the mounting surface electrical contacts, and the other end connected to the second power source region through a layer connecting member passing through the ground layer.
With such a structure, not only can low-frequency noise radiation be reduced for the above-described reason, but also, high-frequency noise radiated from the second power source region can be kept law. Further, because the integrated circuit component and the second power source region can be electrically separated from each other, the second power source region and the integrated circuit component are integrated with each other electromagnetically so as to prevent radiation of noise.
Further, radiation noise leaking from the periphery of the annular slot is prevented from becoming large. Because the area of the annular slot is smaller than a case where the opening area is larger than the mounting face for the integrated circuit component, the radiation noise can be reduced. Because the current loop formed by the second power source region, the auxiliary wires and the integrated circuit component is the smallest, the radiation noise can be suppressed to a low level.
Further, to achieve the above object, according to another aspect of the invention, it is provided a method of reducing electromagnetic noise introduced into a semiconductor device from a power source for the semiconductor device, the method comprising the steps of:
(a) forming a power supply layer having a first power source region surrounding a second power source region electrically isolated from the first power source region, with the second power region having an area smaller than that of the semiconductor device;
(b) supplying power to the first power source region, and from the first power region to the second power region through a filter;
(c) mounting the semiconductor device over the power supply layer with a ground layer disposed between the semiconductor device and the power supply layer; and
(d) supplying power to the semiconductor device through electrical connections extending from the second power source region through the ground layer to the semiconductor device.